The adaptive immune response to pathogens initiated by CD4+ T-cells can take two distinct forms, referred to as humoral and cell-mediated immunity. Factors such as hormones, cytokines, adjuvants and antigen presenting cells (APC) are thought to influence skewing of T-cell responses. Based on preliminary data, the investigator postulates that the form of the antigen (e.g. peptide or protein or microbial-derived) used to prime a CD4+ T-cell will also have a bearing on subsequent responses through the preferential usage of APC subsets. Using both in vivo and in vitro approaches, the investigator will address this issue in two specific aims. The investigator will determine if peptide and protein antigens can induce differential CD4+ T-cell priming through their interaction with different APC, and seeks to identify the APC requirements for microbial-derived and viral-derived antigens during CD4+ T-cell priming.